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HOW DO MUTATIONS CAUSE GENETIC DISORDERS?


HOW DO MUTATIONS CAUSE GENETIC DISORDERS?


anchorman How often do you hear about the discovery of genes responsible for medical conditions such as cancer, diabetes, obesity, Alzheimer's disease or NF1?

It seems like scientists are finding new genes that affect our health just about every day!


anchorwoman

But what does it mean when they "find a gene"?

This means that scientists have identified a gene that causes a medical condition -- but only when it is mutated.

People sometimes assume that "if I have the gene, then I'll get the disease!" This is a common misconception. It's important to understand that all humans have the same genetic blueprint -- which means that we all have the same basic set of genes. The differences you see between you and your best friend, or between people from different continents, result from variations that occur within the sequence of each gene.

So all of us have the genes that are responsible for medical conditions. The medical condition only arises when the correct DNA sequence of the gene is altered (or mutated) in a way that causes the protein encoded by the gene to malfunction.

What happens when a protein malfunctions?

If a protein can't do its job, then cells containing that protein may not function properly. Since humans are composed of cells, a malfunction can lead to medical problems.

Here's another way to think about it!

Think of a cell as a car. A car is made up of many parts, just as a cell is made up of many proteins. Each part -- or protein -- does a specific job. What happens when a part breaks on your car?

It depends. If one headlight burns out, you can still drive the car, although driving at night may be tough. But when your brakes fail, you're really in trouble -- before you know it, your car is cruising out of control! And if you're driving in traffic when this happens, then your car troubles are certain to affect the cars around you, making problems for the whole street.

Proteins in cells work the same way. Some proteins are more important to a cell's normal function than others. A cell might still be able to function properly if the mutated protein isn't that important, like the headlight on your car.

Funding provided by The Children's Tumor Foundation, formerly The National Neurofibromatosis Foundation.
How do we get mutations in our genes?

We can get mutations in several ways:

  1. Mutations can be inherited, or passed from parent to child. This type of mutation is called a germline mutation.
  2. Mutations that arise sporadically throughout our lifetime (in non-sex cells) are called somatic mutations. Most of the time, our cells are very good at fixing somatic mutations when they occur. In the rare instances when they are not repaired, a medical condition may result.
  3. A third type of mutation, called a novel germline mutation, is a combination of a somatic and an inherited mutation. The novel germline mutation arises in a parent's germ cell - either the father's sperm cell or the mother's egg cell. The child conceived through the union of sperm and egg carries the novel germline mutation.

For example, about half of all NF1 cases are thought to arise from inherited mutations. The other half arise from novel germline mutations and are commonly referred to as "spontaneous" mutations.